1. Field of the Invention
The present invention relates to a bar code reader and, more particularly, to a bar code reader used for a POS (point-of-sale) system which is installed on a counter of a store and is used for reading bar codes attached to goods.
2. Description of the Related Art
In POS systems and in physical distribution systems, so far, it has been a widely accepted practice to exactly calculate and manage goods by reading bar codes. The bar codes are attached to the goods and are read by using a bar code reader.
In such a bar code reader, a ray of light such as laser light is emitted onto the bar code, which is attached to the article by printing or the like method. Thus the bar code reader scans the bar code surface, and the laser light reflected by the bar code is detected to read the bar code.
FIG. 1A is a diagram illustrating a conventional bar code reader in a perspective manner so that the internal structure can be seen. The bar code reader employs a source of laser light, such as a semiconductor laser, as a source of light. In FIG. 1A, reference numeral 201 denotes a laser module constituted by a laser beam source and lenses. Reference numeral 202 is a polygon mirror, which is a polyhedral mirror having a plurality of reflection planes. The polygon mirror 202 is rotated by a motor 207. The laser beam emitted from the laser module 201 is reflected by a small plane mirror provided at the center of a concave mirror 203 and arrives at the reflection plane of the polygon mirror 202. The laser beam is reflected by the reflection plane of the polygon mirror 202. Here, however, since the polygon mirror 202 is rotating, the laser beam is scanned, for example, in the clockwise direction in the drawing.
Reference numeral 204 denotes mirrors for splitting the scanning line and on which is incident the laser beam scanned by the polygon mirror 202. The laser beam is downwardly reflected by the scanning line-splitting mirrors 204, upwardly reflected by a bottom mirror 205 of nearly a V-shape, and is emitted through a reading window 206.
The laser beam emitted from the reading window 206 scans the article that passes over the bar code reader. The laser beam, after having scanned the article, is reflected by the surface of the article to which the bar code is attached, and is caused to be incident on the bar code reader through the reading window 206.
Light reflected by the bar code of the article and incident on the bar code reader, is reflected by the bottom mirror 205, scanning line-splitting mirrors 204 and polygon mirror 202, and is caused to be incident on the concave mirror 203. The concave mirror 203 focuses the laser beam reflected and diffused by the bar code toward a light detector 208. The laser beam received by the light detector 208 is decoded by a decoding circuit in the bar code reader and is output to an external unit.
The bar code reader shown in FIG. 1A has only one reading window 206. Such a bar code reader can be installed on an accounting counter in a store in two ways. I.e., the bar code reader is installed so that the reading window 206 is in flush with the surface of the accounting counter, or the bar code reader is so installed that the reading window 206 is nearly vertical to the surface of the accounting counter.
When the bar code reader of FIG. 1A is installed on the accounting counter, there is offered only one reading window 206 as described above. When the article is passed over the bar code reader at the accounting counter to read the bar code attached to the article, the bar code is not scanned by the scanning light unless the bar code faces the reading window 206, and the bar code is otherwise not read out. This is because in conventional bar code readers, a limitation is imposed on the range scanned by the scanning light or on the direction in which the scanning light is emitted.
To solve the above problem, a bar code reader has in recent years been devised having a plurality bf reading windows. Such a bar code reader emits the scanning light through the respective reading windows to scan the article having bar code from a plurality of different directions.
FIGS. 1B and ID illustrate appearances of bar code readers 210 and 220 for which the abovementioned countermeasure is taken. These bar code readers 210 and 220 are provided with reading windows (hereinafter referred to as bottom windows) 216, 226 formed in the bottom surface of the device, and reading windows (hereinafter referred to as side windows) 217, 227 formed in the side surface erected at an angle nearly vertical to the bottom windows 216, 226. Scanning light. is emitted from the bottom windows 216, 226 toward the upper side windows 217, 227. On the other hand, scanning light is emitted in nearly the horizontal direction (toward the operator) from the side windows 217, 227.
As shown in FIGS. 1C and 1E, the difference between the bar code readers 210 and 220 is that the bottom window 216 of the bar code reader 210 has a size of 5 inches.times.4 inches, whereas the bottom window 226 of the bar code reader 220 is of a trapezoidal shape having a size of 6 inches.times.6 inches.
As described above, a plurality of reading windows are provided, and the scanning light is emitted in a plurality of directions through the respective reading windows. Therefore, the article 209 passing on the bar code readers 210, 220 is irradiated with scanning light from a plurality of directions, and the probability for scanning the bar code is enhanced compared with when a bar code reader having only one reading window is used.
FIG. 1F illustrates a calculation counter (check-out counter) 230 on which the above-mentioned bar code reader 220 is installed. On the check-out counter 230 is installed the bar code reader 220. The operator P stands at a position facing the side window 227.
On the upper side of the side window 227 is provided a key board 222 for inputting data related to the goods to which no bar code has been attached. A belt conveyer 233 exists on the upstream side of the check-out counter 230 to carry the goods to the position of the bar code reader 220. Reference numeral 235 denotes a guide plate for guiding the goods onto the bottom window 226 of the bar code reader 220.
As the article is carried to the position of the bar code reader 220 and passes by the bar code reader 220, the bar code is read out irrespective of the direction of the bar code attached to the article. A POS terminal 234 is provided by the side of the operator P, and the calculation processing is executed by the POS terminal 234.
FIG. 1G illustrates a bar code readable area of the bar code readers 210 and 220 of FIGS. 1B and 1D. Here, the hatched region RP represents the region where the scanning beams emitted from the side windows 217, 227 and the bottom windows 216, 226 are focused. In this region, the bar code is read out even when the bar code is turned in the horizontal direction by 360 degrees. Thus, since the scanning beams are emitted from the two reading windows, the bar code readable area is broadened. Besides, even when the bar code surface does not completely face one reading window, the bar code can be read out.
However, even such bar code readers have problems as described below. In the case of the bar code reader 210 shown in FIGS. 1B and 1C, for example, the bottom window 216 has a size of 4 inches.times.5 inches. Thus, the bar code reader 210 shown in FIGS. 1B and 1C has a narrow bottom window 216, and a pattern (hereinafter referred to as scanning pattern) is constituted by a small number of scanning lines emitted. from the bottom window 216.
In the case of the bar code reader 220 shown in FIGS. 1D and 1E, furthermore, the bottom window 226 has a size of 6 inches.times.6 inches, which is larger than the size of the bottom window 216 of the bar code reader 210 shown in FIGS. 1B and 1C. However, the bottom windows 216, 226 are usually constituted by a reinforced glass which resists falling articles, and are, hence, expensive. Therefore, the bar code reader 220 of FIGS. 1D and 1E becomes expensive.
Various optical systems are arranged in a bar code reader, and the arrangement must be so contrived that the reader does not become bulky. However, in the conventional bar code readers and, particularly, in the bar code readers 210, 220 which read the bar code through two surfaces (i.e., through thee bottom windows 216, 226 and the side windows 217, 227), a total of two laser beam sources are provided: a laser beam source for the bottom windows 216, 226 and another laser beam source for the side windows 217, 227. Therefore, arrangement of the optical systems for accomplishing a desirable reading ability involves various limitations and problems, resulting in an increase in the size of the device and an increase in the cost of production.